Weighing apparatus



Nov. 19, 1940. J. H. DE IONGH 2 22 WEIGHING APPARATUS Filed Nov. 9, 19372 Sheets-Sheet l J 797-46 fang;

Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE Application November9, 1937, Serial No. 173,676 In the Netherlands November 14, 1936 4Claims.

This invention relates to weighing apparatus of the known typecomprising a servomotor adapted, under the control of the weighinglever, to displace a travelling poise against which the loadautomatically balances itself, and its primary object is the provisionof improved means whereby oscillations of the weighing lever about itsneutral position, or position of equilibrium are completely or almostcompletely suppressed.

With this object in view, the invention contemplates the provision, inweighing apparatus of the aforesaid type, of a servomotor which, whenoperating, not only displaces the travelling poise, but in additionexerts an auxiliary force on the weighing lever, or on a part associatedtherewith, tending to restore the same into its neutral position. Theaction of this auxiliary force results in a substantial reduction of thetime required for the weighing lever to resume 20 its initial position,which is the position wherein the servomotor is inoperative.

The auxiliary force may be so adjusted that the weighing lever duringits return movement will not, or not appreciably deflect beyond itsposition of equilibrium.

Since the magnitude of the auxiliary force is reduced to zero at themoment wherein the action of the servomotor ceases, this force does notafiect the position of equilibrium of the weighing lever.

. In accordance with this invention, the apparatus may further be soarranged that the magnitude of the auxiliary force varies with thebalancing speed of the servomotor, in such a manner that said force isgradually reduced to zero as the weighing lever' approaches its neutralposition.

In order that the invention may be fully understood by those skilled inthe art, it will be described hereinafter with reference to thediagrammatic drawings, in which:

Fig. 1 shows a side elevational view, partly in section, of weighingapparatus provided with a hydraulic servomotor,

Fig. la is an enlarged sectional view of the distributing valvearrangement shown in Fig. 1.

Fig. 2 is a side. elevational view, partly in section, of a similarweighing apparatus provided 50 with an electric servomotor andmechanical means for transmitting the auxiliary force to the weighinglever,

Fig. 3 is a side elevational view of similar weighing apparatus providedwith an electric 5 servomotor and electrodynamic means for transmittingthe auxiliary force to the weighing lever, and

Fig. 4 is a plan view of the apparatus shown in Fig. 3.

In .r-ig. l, the numeral l designates the double 5 armed beam of theweighing apparatus. Said beam is adapted, when deflecting under theaction of a load suspended therefrom, to actuate a servomotor. Atravelling poise 8 is adapted to be displaced along said beam by theservomotor, 10 thereby tending to restore the beam i into its initial orneutral position.

lhe servomotor here comprises a hydraulic cylinder 5 and a piston 6movable therein. Mounted on the top of this cylinder and (10- axialtherewith is a second cylinder l3, the pis ton it of which is secured tothe rod 1 of the piston 8 and is provided with a narrow passage l2.Provided in the top cover of cylinder i3 is a third, small cylinder, inwhich is a piston ll connected through a rod M with the beam i.

The composite cylinder, formed of the cylin ders 5 and i3, is supportedin an upright position on the bottom of a tank 35 filled with oil oranother suitable fluid. The top cover of the cylinder i3 is provided,below the level of the oil in the tank, with a spring loaded inlet valvel9 and with a spring loaded outlet valve 20, whereas the lower part'ofthe cylinder l3 communicates with the tank it": through a port 6 i Theload is adapted to be suspended from the left hand side arm of the beamI through a rod 2! having a pivotal connection with a substantiallyhorizontal lever 22, the left end of which is hinged to a fixed bracket2 and the right end of which is pivoted to a rod 23 flexibly coupledwith the distributing valve 3 of the hydraulic cylinder 5. Said valve ismovable in a valve casing 3a communicating through ports 4 and 9 withthe cylinder 5, and connected through a pipe i l with the pressure sideof an oil pump not shown. The suction side of the pump is connected tothe tank IS. The distributing valve 3 is formed of a solid rod providedwith recesses 3b as shown more clearly in Fig. 1a.

Secured to the upper end of the piston rod 1 is a rack 24 meshing with apinion 25 keyed to the shaft of a roller 26. Flexible metallic straps 21and 28, which are passed in opposite directions over and secured withtheir one ends to said roller, are led over guide pulleys 29 and 30,respectively, and connected with their other ends to the left and to theright end, respectively, of a bar 3| secured to'the travelling poise 8.The pulleys 29 and 30 are rotatably mounted on the beam I in such amanner that the straps 21 and 28 pass approximately through the axis ofrotation 82 of the beam, so that they cannot exert any turning momentthereon.

Fixed stops 88 and 84 moimted in the vicinity of the right hand side endof beam I limit the deflection of the beam in either direction.

As long as there is no load suspended from the rod 2I, the poise 8assumes an extreme left position on the right hand side arm of beam I,the pistons 8 and I8 are in their top positions, and the beam ishorizontal. When a load is appliedtotherod 2Ithebeamlturnsinacounterclockwise direction so as to engage the limitstop 88. As the rod 2| moved downwardly the lever 22 turns in aclockwise direction so that the rod 28 together with the valve 8 areforced downwardly. In this position of the valve 8 the upper series ofrecesses 8b permit communication between the chamber 40 of the valvecasing and the upper port of the cylinder 8 as shown in Fig. la so thatoil under pressure enters the cylinder 8 through the port 4. Thecylindrical portion of the valve 8 immediately above the lower series ofrecesses 8b prevents the oil under pressure from passing into the lowerport of the cylinder 8 and the lower series of recesses in this positionof the valve 8 allow the fluid within the lower port of the cylinder 8to escape through the port 8 into the tank l8. Thus the piston 8 isforced downwardly whereby the rack 24 turns the pinion 28 and the roller28 in a clockwise direction and the strap 21 pulls the poise 8 to theright.

Simultaneously, the downward movement of the piston I8 reduces thepressure in the upper part of cylinder I8 and thus causes the piston Hto descend. This movement of the piston I1 is transmitted, through therod i8, to the right hand side arm of the beam I. The magnitude of thisdownwardly directed auxiliary force is adapted to be adjusted by varyingthe strength of the spring whereby the inlet valve I8 is loaded. If thetension of said spring has the proper value, the movement of thetravelling poise 8 ceases the moment the beam resumes its horizontalposition of equilibrium. The same result can be attained by properlyadjusting the cross-sectional area of the narrow passage I2. Adjustmentof the spring tension is, however, more convenient.

If the beam I is thereafter unloaded, it will turn in clockwisedirection and the valve 8 will be moved up. As a consequence, thehydraulic piston 8 will be raised, the rack 24 will turn the roller 28in a counterclockwise direction, and the strap 28 will move thetravelling poise 8 to the left. Simultaneously, the piston I'I exerts anupwardly directed thrust on the right hand side arm of the beam I, so asto counteract said deilection of the beam. Proper adjustment of thetension of the spring loading the outlet valve 28 will result in thetravelling speed of the poise 8 being reduced to zero the moment thebeam attains its horizontal position of equilibrium.

The oil supplied-through the pipe I4 to the cylinder 5 escapes into thetank I8, whence it is withdrawn by the oil pump referred tohereinbefore.

In Fig. 2, the travelling poise 8 of the weighing apparatus is adaptedto be displaced along the beam I by a screw spindle 44 driven, through asuitable reduction gear not shown, by an electromotcr 43 mounted on thebeam. The electric circuit of said motor is controlled by the beam motorswitch.

In this modification, the auxiliary force for restoring the deflectedbeam I into a neutral position is supplied by the eiectromotor 48 incooperation with a device comprising a brake cylinder I8 illled with oiland a piston II movable therein. Said piston is provided with a narrow eI2 and is hinged through its rod I8 to apoint intermediate the endsofafloating lever 48. The right end of the lever 48 is suspended through arod 88 from the right hand side arm of the beam I, whereas the left endof the lever 48 is pivoted to a rod 8|, the upper end ofwhichhasarack 82inmesh withapinion 88. This pinion is keyed on the shaft of a worm wheel84 coacting with a worm 88 on the screw spindle 44.

If the load is applied to the left hand side armofbeam I throughtherod2I.itcausesthe beam to turn in a counterclockwise direcflon, therebyclosing the contact 48 and starting the motor 48. Consequently, thescrew spindle 44 isdrivensoastomovethepoise8totheright to balance theload. Simultaneously, the rod 8i and the piston II are moved upwardowing to the rotation of the pinion 88, so that the rod 88 pulls theright hand side arm of the beam I down to its initial position wherebythe contact 48 is broken and the motor 48 is stopped.

If the load is wholly or partly removed the right hand side arm of theweighing beam I defiects downwardly thereby closing the contact 48 andstarting the motor 48 in a reversed direction. Consequently the screwspindle 44 is now driven so as to move the poise 8 to the left and therod 8| is moved downward so that pressure is set up in the cylinder I8below the piston II which exerts an upwardly directed force on the beamI. The beam is, therefore, restored into its neutral position wherebythe contact 48 is broken and the motor 48 is stopped.

In the embodiment shown in Figs. 3 and 4, like parts are designated bythe same references as in Fig. 2. Mounted in bearings of the beam I is ashaft 88 transversely to the screw spindle 44. Said shaft is coupledthrough gear wheels 81 and 88 with said spindle and carries at its freeend a disk 88 of non-magnetic metal. Opposite this disk is a stationarydisk 88 provided with a circular series of permanent magnets adapted toinduce eddy currents in the revolving disk 88, thereby braking the sameso as to exert on the beam I a turning moment, which tends to restorethe beam into a neutral position. The magnitude of this moment increasesand decreases with the rotary speed of the disk 88, or with the rotaryspeed of the servomotor 48, and is reduced to zero the moment said motorstops.

If a load is applied to the left side arm of the beam I it turns in acounterclockwise direction, thereby closing the contact 48 and startingthe motor 48. Consequently, the screw spindle 44 is driven so as to movethe poise 8 to the right to balance the load and the disk 88 exerts onthe beam a turning moment which tends to turn the beam back to itsneutral position. Thereby contact 48 is broken and the motor 48 isstopped.

If the load is wholly or partly removed the right arm of the weighingbeam I deflects downwardly thereby closing the contact 48 and startingthe motor 48 in a reversed direction. The screw spindle 44 is now drivenso as to move the poise 8 to the left and the disk 89 is also rotatedder having a distributing valve associated with said lever, a pistonmovable in said hydraulic cylinder, means operatively connecting saidpiston with said poise, a second piston connected to said first pistonand movable in a second cylinder filled with liquid, a third cylindercommunicating with said second cylinder and having a third pistonmovable therein so as to cooperate with said second piston, and meansconnecting said lever with said third piston.

2. In a weighing apparatus, a weighing lever, a travelling poise on saidlever, a hydraulic cylinder having a distributing valve, meansoperatively connecting said lever with said valve, a piston movable insaid hydraulic cylinder, means operatively connecting said piston withsaid poise, a second piston connected to the first piston and movable ina second cylinder filled with liquid and provided with spring loadedinlet and outlet valves, a third cylinder communicating with said secondcylinder and having a third piston movable therein so as to cooperatewith said second piston, and means connecting said lever with said thirdpiston.

23. In weighing apparatus, a weighing lever, a travelling poise on saidlever, a. servomotor controlled by deflection of said lever, meansactuated by the servomotor for displacing the poise on said lever, andmeans continuously coupled to the servomotor and actuated thereby tocontinuously exert an auxiliary force on said lever for restoring thesame to a neutral position when the servomotor is actuated by deflectionoi the weighing lever.

4. In weighing apparatus as claimed in claim 3 wherein the means forcontinuously exerting the auxiliary force is so connected to theservomotor that the magnitude of the auxiliary force on the weighinglever varies with the speed of the servomotor.

JOHAN H. DE IONGH.

